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Monday, 23 April, 2001, 03:49 GMT 04:49 UK
St John's wort used in cancer fight
St John's wort
St John's wort contains a light sensitive chemical
By Marlene Smits

A light sensitive substance taken from the herb St John's wort is being used to treat cancer.

Belgian scientists have already used the substance, hypericin, to detect cancer cells.

But they also believe hypericin could be used to actually kill off cancerous tumours.

The research involving the St John's wort extract, hypericin, holds promise

Imperial Cancer Research Fund
Professor Peter de Witte, from Leuven University in Belgium, has been perfecting a technique known as Photodynamic Therapy (PDT) for the last nine years.

It works by utilising the light sensitive properties of hypericin to show up the presence of cancer cells.

He said: "We've discovered that especially bladder tumours that can't be detected through endoscopy, can be detected with hypericin."

The technique is currently being used to treat 100 patients in Belgium.

At present, surgery is required to remove cancer cells once they have been located.

But Prof de Witte is working on a new application of PDT to destroy tumours.

Endoscopic tube

PDT works by injecting hypericin into a patient through an endoscopic tube with a camera on the end.

After inserting the hypericin the tumours light up red in blue light as a result of the fluorescing effect of hypericin.

Tests with mice have proven that the hypericin selectively gathers itself in the tumour and not in surrounding tissue.

Dr Els Delaey has worked on the research with Prof de Witte.

He said: "We have investigated and experimented with many different light sensitive substances both natural and synthetic, but we came to the conclusion that special substances in St John's wort work best for the light therapy."

The researchers have now gone one stage further in preliminary tests on mice.

They have shown that PDT and hypericin can be used in combination with laser therapy to kill off tumours.

When hypericin is injected in the mice it automatically finds its way into the tumour.

If the tumour is then subjected to a laser, the combination of light, oxygen and hypericin produces a chemical reaction.

This creates reactive oxygen which can effectively dissolve the tumour.

By using small laser beams the work can be done very precisely so that healthy cells are not damaged.

Hypericin makes it possible to detect cancer in problematic areas.

It also raises the possibility of effective treatment without the unpleasant side effects associated with chemotherapy.

Promising treatment

A spokesman for the Imperial Cancer Research Fund told BBC News Online PDT showed great promise in treating cancer.

He said: "There are several light sensitive drugs used in PDT, some of which have been used to treat skin cancer with great success.

"The problem with any form of PDT is targetting the therapy so it acts on the tumour only.

"So photosensitive drugs that accumulate selectively in tumour tissue are good news, because they avoid making the whole patient sensitive to light - a side effect that can last for weeks, depending on the drug.

"The research involving the St John's wort extract, hypericin, holds promise and it may be a particularly useful light sensitive substance for bladder tumours.

"However, it may well be some time before the research can be transferred from mice models to be used effectively in the clinic."

Annie Angle, senior information nurse for the Cancer Research Campaign, said: "Anything that raises the possibility of effective treatment for cancer patients is welcome.

"But this is still very early stage research and we need further trials before we can tell whether this is going to be effective."

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